This invention relates generally to a steering mechanism for an agricultural tractor in which the front axle is laterally shiftable in response to a steering movement of the steerable wheels and, more particularly, to an oscillation stop mechanism that is cooperable with the laterally shiftable axle to limit the amount of oscillatory pitching movement throughout the entire range of lateral shifting movement of the axle.
Tractors, whether used in an agricultural setting or in an industrial setting, typically include a fixed axle through which primary driving power is transferred through fixed wheels rotatably mounted on opposing ends of the fixed axle, and a steering axle having pivotally mounted steerable ground engaging wheels rotatably mounted on the opposing ends thereof to support the chassis of the tractor above the ground. Supplemental driving power is often provided through the steerable ground engaging wheels, while a steering mechanism remotely controllable by the operator from the operator's compartment selectively controls the pivotal movement of the steerable wheels relative to the steering axle.
One such steering mechanism incorporates a transversely disposed, horizontally extending hydraulic cylinder supported by the steering axle and connected to the opposing steerable wheels. This hydraulic cylinder affects pivotal movement of the steerable wheels about their respective pivotal connections to the steering axle by manipulating the pressures in the hydraulic cylinder to effect a transverse displacement of the cylinder rod, causing a turning of the wheels.
Due to physical limitations relating to the range of movement of the steering mechanism and to the eventual interference between the steerable wheels and the steering axle or chassis frame, the amount of pivotal movement of the steerable wheels relative to the steering axle is limited by tire size and track setting to a given restricted turning angle. This maximum turning angle defines the minimum turning radius of the tractor for a given chassis clearance width, axle oscillation angle, wheel base length and king pin spacing. The selection of the length of the wheel base, i.e., the distance between the fixed axle and the steering axle, is a compromise between the need to minimize the turning radius and, therefore, minimize the wheel base length, and to maximize ride considerations which require longer wheel base lengths.
Further complicating the development of a steerable axle to improve turning characteristics of vehicles such as agricultural tractors is the requirement of accomodating the oscillatory pitching movement associated with such vehicle axles. The limits imposed on the structural components to stop the pitching motion of the axle relative to the chassis must be effective throughout the entire range of lateral shifting movement provided to the steerable axle. In some instances where the tractor tires are closely spaced and less than a full turn is being attempted, there is very little clearance between the tire and the chassis sheet metal; however, when tight turns are being made the tire is sufficiently displaced from the chassis sheet metal that adequate clearance exists to allow a normal oscillation range. Accordingly, it would be desirable to provide a mechanism to vary the permissible oscillatory movement of the axle as a function of the degree of turn being attempted.